The new Office of Sanctions Enforcement will open in Brussels next month with a mandate its predecessors never had: to trace, in real time, the corporate chains through which restricted goods reach restricted buyers.

Enforcement has been the union''s weakest muscle. Officials estimate that as much as a fifth of restricted trade has moved through intermediaries in third countries. The new office will not close every gap — unanimity rules still bind the member states — but it moves the argument from naming ships to auditing supply lines.